The present invention relates to a variable performance valve train used in internal combustion engines. More particularly, the present invention pertains to a variable performance valve train having three-dimensional cams, the profile of which continuously changes along the axis of a camshaft.
Japanese Unexamined Patent Publication No. 5-125966 discloses a first prior art apparatus, which includes a variable valve lift mechanism. The variable valve lift mechanism includes intake and exhaust valves, which are driven by camshafts, and low speed and high speed cams for driving the intake valves or the exhaust valves. The mechanism varies the valve lift, or the valve open angle, of the intake valves or the exhaust valves. In this specification, the valve open angle refers to an angle of rotation of a crankshaft during which an intake valve or an exhaust valve is open.
When there is a malfunction in the control of a throttle valve, the mechanism of Japanese Unexamined Patent Publication No. 5-125966 selects a set of cams that will decrease the engine power. Specifically, the mechanism uses either high speed cams or low speed cams such that the vehicle speed is reduced.
Instead of having two types of cams, a variable performance valve train according to a second prior art apparatus has three-dimensional cams, the profile of which continuously changes along the axis of a camshaft. However, unlike the prior art apparatus of Japanese Unexamined Patent Publication No. 5-125966, a valve train having three-dimensional cams cannot employ the valve switching control and fail-safe control for decreasing the engine power.
For example, if the mechanism having the three-dimensional cams simply decreases engine power for performing fail-safe control, engine starting is hindered or engine speed stability deteriorates.
A valve train according to a third prior art apparatus disclosed in Japanese Unexamined Patent Publication 8-177434 includes the high speed and low speed cams of Publication No. 5-125966 and a variable valve timing mechanism. The variable valve timing mechanism adjusts the rotational phase of the camshaft.
When either the variable valve lift mechanism or the variable valve timing mechanism malfunctions, the variable valve lift mechanism uses the low speed cams, and the variable valve timing mechanism retards the rotational phase of the camshaft. This prevents the intake valves from interfering with the pistons and the exhaust valves.
A malfunction of the variable valve lift mechanism could be either a malfunction of the low speed cams or a malfunction of the high speed cams. In order to perform fail-safe control, different programs must be prepared for a malfunction of the low speed cams and for a malfunction of the high speed cams. The two fail-safe controls increase the time and effort required to make the programs and increase the required memory capacity for storing the programs.
If the variable valve lift mechanism malfunctions when the high speed cams are being used, the mechanism may not be able to switch to the low speed cams. In this case, engine starting and engine speed stability will deteriorate.
Accordingly, it is an objective of the present invention to provide a variable performance valve train that facilitates engine starting and stabilizes the engine speed when there is a malfunction thereby making it easier for the driver take steps to correct the malfunction.
To achieve the above objective, the present invention provides a valve train for an internal combustion engine, comprising: a variable valve performance mechanism for continuously changing the valve open angle of at least one of an intake valve and an exhaust valve; a controller for controlling the variable valve performance mechanism; a sensor for detecting the running state of the engine; and a judging device for judging whether there is a malfunction in the engine based on a detection signal of the sensor, wherein, when the judging device judges that there is a malfunction in the engine, the controller actuates the variable valve performance mechanism to decrease valve overlap.
The present invention further provides a valve train for an internal combustion engine, comprising: a variable valve performance mechanism for continuously changing the valve open angle of an intake valve; a controller for controlling the variable valve performance mechanism; a sensor for detecting the running state of the engine; and a judging device for judging whether there is a malfunction in the engine based on a detection signal of the sensor, wherein, when the judging device judges that there is a malfunction in the engine, the controller actuates the variable valve performance mechanism to advance the closing timing of the intake valve.
The present invention provides a valve train for an internal combustion engine, comprising: a variable valve performance mechanism for continuously changing the valve open angle of an exhaust valve; a controller for controlling the variable valve performance mechanism; a sensor for detecting the running state of the engine; and a judging device for judging whether there is a malfunction in the engine based on a detection signal of the sensor, wherein when the judging device judges that there is a malfunction in the engine, the controller actuates the variable valve performance mechanism to retard the opening timing of the exhaust valve.
The present invention further provides a method for changing the valve performance of at least one of an exhaust valve and an intake valve by using a three-dimensional cam, the method comprising: detecting the running state of an engine; judging whether the engine is running normally based on the detected running state; controlling a valve open angle based on the detected running state when the engine is judged to be running normally; and decreasing valve overlap when the engine is judged to be running abnormally.
The present invention provides a method for changing the valve performance of an intake valve by using a three-dimensional cam, the method comprising: detecting the running state of an engine; judging whether the engine is running normally based -on the detected running state; controlling a valve open angle based on the detected running state when the engine is judged to be running normally; and advancing the closing timing of the intake valve for performing a failsafe when the engine is judged to be running abnormally.
The present invention further provides a method for changing the valve performance of an exhaust valve by using a three-dimensional cam, the method comprising: detecting the running state of an engine; judging whether the engine is running normally based on the detected running state; controlling a valve open angle based on the detected running state when the engine is judged to be running normally; and advancing the closing timing of the exhaust valve when the engine is judged to be running abnormally.
The present invention provides a valve train for an internal combustion engine, comprising: an axially movable camshaft rotatably supported on the engine; a three-dimensional cam located on the camshaft to selectively open and close a valve, wherein the profile of the three-dimensional cam continuously changes in the axial direction; an actuator for axially moving the camshaft to change at least the valve lift of the valve lift and the valve timing of the valve; a fluid pressure source for generating fluid pressure to actuate the actuator; and a control valve for adjusting the position of the camshaft by controlling fluid pressure supplied to the actuator from the fluid pressure source; wherein a default position toward which the camshaft is moved when the control of fluid pressure by the control valve is stopped is the same as a default position toward which the camshaft is moved when the fluid pressure source is not supplying fluid pressure to the actuator.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.